I'm not entirely sure what you mean by "reinforcing word".  If you mean that when the dog does what you ask, you say a scripted word, like "Good dog!", then the best thing to do is to give a treat after you say it.  Every time at first, so that they associate hearing the words with getting a treat, and then gradually get more unpredictable -- sometimes you say it and give a treat, and sometimes you say it and don't give one .(This is the same principle as slot machines - you don't know when you'll win on one, but you know it's gotta happen sometime, so you keep playing). 

You'll never be able to get rid of treats entirely -- dogs love treats, and it's a nice gesture to reward them every once in a while!